As more carriers become available and traffic increases, operators are increasing the number of carriers in their networks. A functionality referred to as increased monitoring (IncMon) in both Third Generation Partnership Project (3GPP) Universal Terrestrial Radio Access (UTRA) (25.133) and Long Term Evolution (LTE) (36.133 Release 13) specifications facilitates performing measurements on an increased number of carriers. IncMon was developed in response to the increased number of carriers an operator uses. For example, if a user equipment (UE) attempts to measure all carriers with the same priority, the measurement delay might be very large for all carriers. IncMon identifies the carriers that are more important to have a short measurement delay and those that are less delay sensitive (e.g., carriers with a lower probability that they are needed for coverage).
Without IncMon functionality, a UE operating according to the UTRA specification is required to perform measurements on cells distributed on at least two inter-frequency carriers in addition to the cells on the serving carrier frequency (intra-frequency carrier). This requirement may limit an operator's practice of attempting equal usage of all available carriers. For example, this requirement may cause problems when deploying low power node cells (e.g., pico or femto-cells) on a separate carrier (dedicated carrier). A carrier frequency (also referred to simply as a carrier or a frequency) may also be referred to as a frequency layer (or simply layer). A Global System for Mobile (GSM) layer comprises 32 GSM carriers. For other 3GPP radio access technologies (RATs), such as LTE, a layer equals the carrier frequency. Measuring on several carriers at the same, or overlapping, time may be referred to as multiple layer monitoring or measurement. The term monitoring herein may refer to performing one or more measurements on one or more carrier frequencies.
In E-UTRAN specifications, the UE is required to perform measurements on cells distributed on at least 3 inter-frequency carriers (i.e., 3 for E-UTRA frequency division duplex (FDD) and 3 for E-UTRA time division duplex (TDD)), in addition to the cells on the serving carrier frequency. This may be a significant limitation given the amount of spectrum that operators typically have and their advanced deployment scenarios, like heterogeneous networks, as described below.
In both UTRAN and E-UTRAN, when IncMon is not supported, the UE is limited in the total number of carriers that the UE is required to measure. In both systems the UE is required to measure up to 7 non-serving carriers, including inter-frequency and inter-RAT carriers. This requirement is specified for measurements in a low activity radio resource control (RRC) state (e.g., idle state, idle mode, CELL_PCH state, URA_PCH state, etc.) as well as in a high activity RRC state (e.g., connected, CELL_DCH, CELL_FACH states). Examples of inter-RAT carriers in UTRAN FDD belong to GSM/GERAN, UTRA TDD, E-UTRA FDD and E-UTRA TDD systems. Examples of inter-RAT carriers in E-UTRAN FDD belong to GSM/GERAN, UTRA FDD, UTRA TDD, E-UTRA TDD, CDMA 2000 and HRPD systems.
A heterogeneous network is based on a multilayered deployment of a high power node (HPN), such as macro base station (BS) (wide area BS serving a macro cell), and a low power node (LPN), such as pico BS (local area BS serving a pico cell). Other examples of LPNs are home BS serving femto cell or medium range BS serving a micro cell. The LPNs and HPNs may operate on the same frequency (e.g., co-channel heterogeneous deployment) or on different frequencies (e.g., inter-frequency, multi-carrier or multi-frequency heterogeneous deployment).
For a heterogeneous deployment on several carriers, adding neighbor cell information in the macro network may not be possible because two of the inter-frequencies are already used in the macro network. Thus, the mobile will not perform cell-reselection or any kind of cell change (e.g., handover) when entering the coverage area of the LPN.
Based on these new deployment scenarios, a purpose of IncMon is to add new carriers without increasing measurement delays to the most sensitive carriers. With this function the measurement delay of the “normal” set of carriers provides similar delay as for the case with a limited number of carriers. The set of carriers with reduced requirements share a smaller part of the measurement resources between each other. Therefore, the measurement delay may be long. The result is that a UE is able to control these carriers but not able to make a fast cell reselection or handover based on these measurements.
Another consideration of network operators is conserving power consumption. Power consumption is important for UEs using battery or an external power supply. Its importance increases with the continued growth of device populations and more demanding use cases. The importance may be illustrated by following scenarios.
As an example, for machine-to-machine M2M operation (e.g., sensors that run on battery), on-site exchange (or charging) of the batteries for a large amount of devices is a major cost. The battery lifetime may even determine the device's lifetime if it is not foreseen to charge or replace the battery. Even where UEs may consume power from an external power supply, consuming less power may be desirable for energy efficiency purposes.
Enhancing discontinuous reception (DRX) operation is one way to improve battery consumption in a UE. DRX makes the UE reachable during pre-defined occasions without resulting in unnecessary signaling. As currently defined, DRX cycles in LTE can at most be 2.56 seconds. This cycle duration may not allow for sufficient power savings for UEs that only need to wake-up infrequently (e.g., every few or tens of minutes) for data. Hence, DRX cycle extension may be used to enable significant battery savings for such UEs. Furthermore, the DRX cycle can be set depending on the data delay tolerance and power saving requirements, thus providing a flexible solution for achieving significant UE battery savings. With the extended DRX functionality, the DRX cycle may be extended to be, for example, up to 1 or several hours. There may also be a few “short” DRX cycles active where the UE can be paged (e.g., when in IDLE state). The UE can go to deep sleep during a long period (extended DRX) until it wakes up for the next set of paging intervals with short DRX cycle.
When multiple carriers are in use, during the extended DRX the UE can measure all configured carriers during the set of short DRX cycles. Measurements from the previous set of short DRX cycles may be too old to use for an accurate averaging of different samples over time. Instead, several measurement samples may be needed from each set of short DRX cycles. Therefore, during the few short DRX cycles, all carriers may need to be measured several times to achieve accurate measurement averaging to enhance measurement performance, especially in fading conditions.
3GPP defines eDRX operation for UEs in CONNECTED mode in LTE and for UEs in IDLE mode in LTE and UTRA. In LTE, the eDRX in IDLE is based on the hyper-system frame number (H-SFN) concept. More details on H-SFN are provided below.
For CONNECTED mode, the DRX cycle may extend up to 10.24 s. FIGS. 1A and 1B illustrate examples of the extended DRX cycle.
FIG. 1A is an example enhanced discontinuous reception (eDRX) configuration. The horizontal axis represents time. The illustrated example includes a short DRX period (TDRX) followed by an extended DRX period (TeDRX). The short DRX period includes a sequence of short on-durations 10 separated by short off-durations. The extended DRX period includes a sequence of long on-durations 12 separated by long off-durations.
FIG. 1B is another example enhanced discontinuous reception (eDRX) configuration. The horizontal axis represents time. The illustrated example includes an extended DRX period (TeDRX). The extended DRX period includes a sequence of long on-durations 12 separated by long off-durations. One long on-duration includes a short DRX period (TDRX). The short DRX period includes a sequence of short on-durations 10 separated by short off-durations.
In idle mode, the H-SFN may extend the current SFN range, which is limited to 0 to 1023. An example is depicted in FIG. 2A.
FIG. 2A illustrates an example hyper-system frame number (H-SFN) cycle. The horizontal axis represents time. The illustrated example uses 10 bits of extension, where each hyper SFN contains 1024 SFNs, and therefore spans across 10.24 seconds. For example, H-SFN 0 includes 1024 SFNs spanning 10.24 seconds, following by H-SFN 1 that also includes 1024 SFNs, and so on up to H-SFN 1023, where the cycle repeats at H-SFN 0.
For extended idle mode DRX, the paging frames for the UE consist of: (1) H-SFN value or values that provide the hyper frame/frames at which the UE may be paged (i.e., the paging hyper-frames (PH)); and (2) SFN value or values that provide the legacy frame/frames at which the UE expects to be paged within each paging hyper-frame. The legacy paging frames are within a paging window (PW). An example is illustrated in FIG. 2B.
FIG. 2B illustrates an example of H-SFN based paging for eDRX. The horizontal axis represents time. The extended DRX period (TeDRX) includes an H-SFN cycle as described with respect to FIG. 2A. The extended DRX period includes a paging hyper-frame at H-SFN-X. H-SFN-X includes normal DRX cycle (TDRX). The normal SRX cycle includes paging frames (PF) where the UE may be paged within the hyper frame H-SFN-X.
In eDRX for UTRA (for IDLE UEs), the eDRX cycle is prolonged to between 10 s and up to several hours, which is much longer than the legacy DRX cycles. The DRX cycle consists of a long sleep period, then the UE wakes up to a Paging Transmission Window where there are N_PTW paging occasions with the legacy PS DRX cycle. An example is illustrated in FIG. 3.
FIG. 3 illustrates an example eDRX in UTRA. The horizontal axis represents time. The eDRX cycle includes long sleep periods 16 and paging transmission windows (PTWs) 14. A UE wakes up during PTW 14, which includes a plurality of paging occasions 18 according to a legacy PS DRX cycle.
Next generation of mobile systems (e.g., 5G) may include very long DRX cycles. For 5G downlink transmissions, the rate of symbols to measure in time on each carrier may be low. In some cases, the rate may be as low as one sequence every 100 ms. Because all the carriers may not be synchronized, each measurement sample in 5G will take a long time. Delays will further increase when the measurements on existing 3GPP RATs are added to the new set of carriers for 5G.
The DRX operations described above have particular disadvantages when a user equipment measures on multiple carriers. For example, the number of measurement samples for each set of DRX cycles is large and the time for performing the measurements is limited.
As another example, IncMon may not be compatible with extended DRX because the delay between the extended DRX cycles may be too long. Averaging between the extended DRX cycles may not be accurate because the user equipment may have traveled a considerable distance between extended DRX cycles.
As another example, the extended DRX is intended to save power. Always measuring many carriers in extended DRX, however, may not result in power savings.
The alternatives described in the Background section are not necessarily alternatives that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the alternatives described in the Background section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in the Background section.